Detectives released new footage on Monday of the moments leading up to the lethal attack in a South Yarra street just after 11pm on Friday.

Two men were fighting on the corner of Essex and Malvern roads with one aged in his 40s repeatedly stabbed in the upper body with a bladed weapon.

He was rushed to hospital but later died.

His attacker fled the scene.

In one of the CCTV videos, the killer is knocked down after jumping in front of a motorised scooter on Malvern Street.

The rider takes evasive action and avoids falling off before pulling over briefly and noticing the man had picked himself up.

Detective Inspector Dean Thomas said the traffic incident took place about one or two minutes before the stabbing.

Minutes later, a white van drives by in the opposite direction as the victim moves along the road to stay away from his attacker.

Insp Thomas said that's where the stabbing took place.

"It's quite clear our victim is doing what he can to try and maintain distance," he told reporters on Monday.

Police want to speak to both the scooter rider and van driver to gather an accurate description of the suspect.

Insp Thomas said police were not interested in the rider's potential traffic offence or if the driver had a lawful reason to be out past the city's 9pm to 5am curfew.

The attacker was also caught on CTTV walking near Essex Street about 10 minutes before the stabbing.

He appears to be wearing a Nike jacket and Insp Thomas described him as younger than the victim.

Investigators haven't established if the attack was random, although the victim was known to police.

"It's difficult for me to say whether it's opportunistic or whether our offender knows our victim," Insp Thomas said.

Anyone with dash-cam footage or in the area at that time with information on the stabbing is also encouraged to contact police

"There is somebody out there, I'm pretty confident, from that general area that will know this male," Insp Thomas said.

"We're very keen to identify who this person is, so that male can be held to account for his actions.

"Our victim deserves that."

Australian Associated Press